This application claims the priority benefit of Taiwan application serial no. 91100721, filed Jan. 18, 2002.
1. Field of Invention
The present invention relates to a substrate board structure. More particularly, the present invention relates to a substrate board structure that has a high bonding quality.
2. Description of Related Art
In this information networking age, many electronic products have become indispensable working tools for conducting some of our daily activities. In general, a silicon chip is at the core of most of our electronic products. The chip is electronically connected to other chips or passive devices through a substrate board. The chip and the substrate board are electrically connected together through a lead frame. Typically, the lead frame and the substrate board are bonded together using surface mount technology (SMT). Passive devices may be attached to a chip using surface mount technology as well. However, some of the solder paste may bleed out during an SMT operation.
FIG. 1 is magnified top view showing a contact region on a conventional substrate board. FIG. 2 is a cross-sectional view along line Ixe2x80x94I of the substrate board in FIG. 1. The substrate board 100 is a composite layer comprising a metallic layer 110, a core layer 120, a first solder mask layer 130 and a second solder mask layer 140. The core layer 120 may also be a composite layer comprising a plurality of alternately stacked patterned circuit layers (not shown) and insulation layers (not shown). The core layer 120 further has a first surface 122 and a corresponding second surface 124. The superficial layer just below the first surface 122 is an insulation layer. The metallic layer 110 is formed over the first surface 122 of the core layer 120. The metallic layer 110 includes at least a contact pad 112 and at least a circuit line 114. The contact pad 112 and the circuit line 114 are formed together in a single step. The contact pad 112 has a rectangular outline. The metallic layer 110 can be a copper layer. The first solder mask layer 130 is formed over the metallic layer 110 and the first surface 122 of the core layer 120. The first solder mask layer 130 has an opening 132 that exposes the contact pad 112, a portion of the circuit line 114 close to the contact pad 112 and the first surface 122 of the core layer 120 close to the contact pad 112. The second solder mask layer 140 is formed on the second surface 124 of the core layer 120.
To prepare for a surface mount operation, a solder paste 150 is coated over the central area of the contact pad 112. The contact pad on an electronic device (not shown) is flipped over to make contact with the solder paste 150. A reflow process is next conducted inside an oven (not shown) so that the contact pad on the electronic device and the contact pad 112 are bonded together through the melted solder paste 150. Since surface tension between the solder paste 150 and the copper layer is small, a portion of the solder paste material 150 may disperse along circuit line 114 direction rather than converging on the contact pad 112. Some of the solder paste material may even flow to the first surface 122 of the core layer 120 and lead to unwanted electrical interference and surface contamination. Thus, bonding quality of the surface mounted package is frequently compromised.
Accordingly, one object of the present invention is to provide a substrate board structure capable of improving bonding quality between the substrate board and an electronic device.
A second object of this invention is to provide a substrate board structure capable of eliminating as much interference and contamination due to bonding as possible.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a substrate board. The substrate board comprises a core layer, a metallic layer, a connective metallic layer, a first metal plug and a second metal plug. The core layer is an insulation layer having a first surface and a second surface. The core layer further has at least a first opening and at least a second opening. Both the first opening and the second opening run through the core layer. The metallic layer is formed over the first surface of the core layer. The metallic layer includes at least a contact pad and at least a circuit line. The contact pad and the circuit line are separately lain on the first surface of the core layer. The contact pad has a first through-hole while the circuit line has a second through hole. The first through hole of the contact pad and the first opening in the core layer are connected. The second through hole in the circuit line and the second opening in the core layer are also connected. The connective metallic layer is formed over the second surface of the core layer. The connective metallic layer has a third through hole and a fourth through hole. The third through hole in the connective metallic layer and the first opening in the core layer are connected. The fourth through hole in the connective metallic layer and the second opening in the core layer are connected. The first metal plug fills the first through hole, the first opening and the third through hole so that the contact pad and the connective metallic layer are electrically connected. Similarly, the second metal plug fills the second through hole, the second opening and the fourth through hole so that the circuit line and the connective metallic layer are electrically connected.
According to one preferred embodiment of this invention, the core layer can be a composite layer having a plurality of alternately stacked insulation layers and patterned circuit line layers. In addition, the contact pad may have a rectangular shape or circular shape. The first through hole may be positioned in a middle or peripheral section of the contact pad. The second through hole may be positioned at a terminal region or a middle section of the circuit line.
This invention also provides an alternative substrate board structure. The substrate board comprises a core layer, a metallic layer on the surface of the core layer and a connective metallic layer. The metallic layer includes at least a contact pad and at least a circuit line. The contact pad and the circuit line are separately lain over the first surface of the core layer. The connective metallic layer is enclosed within the core layer such that the connective metallic layer connects electrically with both the contact pad and the circuit line.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.